Conventionally, systems that manage (monitor, control) an air conditioner and a lighting device and the like are placed in a building or a house. Examples of such systems are (i) a large-scale air conditioning system (upper-level system) that includes a central control device, several outdoor devices, and several tens of indoor devices, and (ii) an intermediate and small scale air conditioning system (lower-level system) that includes an outdoor device and several indoor devices.
Such upper-level systems and lower-level systems often have differences not only in the scale but also in the protocol. Hence, it has been known a method of connecting both systems through a relay device provided with a protocol conversion function.
For example, Patent Literature 1 discloses an invention of connecting an air conditioner using a different protocol to a central management system including a central management device that manages multiple equipment instruments through a relay device (equipment instrument adaptor).
In addition, Patent Literature 2 discloses an invention of connecting a field bus (lower-level system in which outdoor devices and indoor devices are connected via local bus) using a different protocol to an upper-level bus (bus of upper-level system) of a network system through a relay device (converter).